I am trying to call the function 'Checks' at the end of my button function, so that the 'Checks' function is able to check the value of labels in the app, and change the background colour, based off the value of the labels that were manipulated within the GoButton function. e.g. if the weather is 'Cloudy', then I'll display some rain clouds, and hide the sun, and hide the rain. Now, when I press the button, the button works fine, but the Checks function is not called, I then have to press the same button a second time, to get it to call?
I have tried placing the self.Checks() line above the catch, and outside of it, but it makes no difference, I still have to press the GoButton twice to get it to have an affect, and change the background.
Button Function:
//Go Button in Main View Controller
#IBAction func GoButton(_ sender: Any) {
//text IS EQUAL TO WHAT IS IN THE TEXT BOX
let text: String = userValue.text!
//API URL TO FETCH JSON DATA
guard let APIUrl = URL(string: "https://api.openweathermap.org/data/2.5/weather?q=" + text + "&appid=***API***KEY***&units=Metric") else { return }
URLSession.shared.dataTask(with: APIUrl) { data, response, error in
guard let data = data else { return }
//JSON DECODER
let decoder = JSONDecoder()
do {
let weatherData = try decoder.decode(MyWeather.self, from: data)
if (self.MainLabel != nil)
{
if let gmain = (weatherData.weather?.first?.main) { //using .first because Weather is stored in an array
print(gmain)
DispatchQueue.main.async {
self.MainLabel.text! = String (gmain)
}
}
}
} catch {
print("Error in fetching data for your location: \(error)")
}
}.resume()
self.Checks()
}
Checks Function:
func Checks() {
//For some reason, this function doesn't get called on the first time you press the button? <<<<<<<<<<<<<<<<<<<<<
if (MainLabel.text! == "Rain") {
rainClouds.isHidden = false
rain.isHidden = false
sun.isHidden = true
} else if (MainLabel.text! == "Drizzle") {
rainClouds.isHidden = false
rain.isHidden = false
sun.isHidden = true
} else if (MainLabel.text! == "Clouds") {
rainClouds.isHidden = false
rain.isHidden = true
sun.isHidden = true
} else if (MainLabel.text! == "Cloudy") {
rainClouds.isHidden = false
rain.isHidden = true
sun.isHidden = true
}
}
Your issue is that you call self.Checks() in the wrong place. You are calling it long before the data is loaded (do some research on asynchronous calls). Move it to inside the completion handler where you set the label's text.
DispatchQueue.main.async {
self.MainLabel.text! = String (gmain)
self.Checks()
}
Unrelated but it is standard practice that function names, variable names, and enum cases start with lowercase letters. Class, struct, and enum names start with uppercase letters.
You have two places in your function that silently return when the guard conditions fail. I would tuck log statements in those blocks to see which one is causing it to exit prematurely the first time you call the function, and then you can work on why.
As a side note, I would also recommend using more descriptive function names, and ones that can't be confused with variable or object names.
Related
I have a button setup so that it saves a CK record based on a users choice from a different part of the UI. Once the function is called the CKRecord is saved in a variable. The next operation the code should take is unwrapping that variable and using it to edit and save the CK record. The Issue is the function I call first, loadChallengeRecord(), isn't the first operation made when the button is pressed. Instead the unwrapping function is run first which is causing the program to exit the unwrap function because the record is nil, and then the loadChallengeRecord() function is called late. Here is the example:
func loadChallengeRecord() {
if let unwrapped = existingChallengeToDetails {
recordID = CKRecord.ID(recordName: unwrapped, zoneID: zone)
publicDatabase.fetch(withRecordID: recordID!) { (record, error) in
if record != nil {
self.currentChallenge = record
} else {
print("error fetching challenge record from server")
}
}
}
}
#IBAction func btnVote(_ sender: Any) {
// load record and save it to var existingChallengeToDetails
loadChallengeRecord()
if let unwrapped = existingChallengeToDetails { }// edit and save record
else { // error }
What am i doing wrong? How can i fix this? Can I denote a priority for these functions to run?
Write your function with completion handler like this
func loadChallengeRecord(completion:#escaping ()->Void) {
if let unwrapped = existingChallengeToDetails {
recordID = CKRecord.ID(recordName: unwrapped, zoneID: zone)
publicDatabase.fetch(withRecordID: recordID!) { (record, error) in
defer { completion }
if record != nil {
self.currentChallenge = record
} else {
print("error fetching challenge record from server")
}
}
}
}
Use it like this ... when it returns completion you can do other stuff dependent on this
loadChallengeRecord {
// do your stuff here
}
The easiest solution is to do the things you have to do in the (asynchronous) completion handler
func loadChallengeRecord() {
guard let unwrapped = existingChallengeToDetails else { return }
recordID = CKRecord.ID(recordName: unwrapped, zoneID: zone)
publicDatabase.fetch(withRecordID: recordID!) { (record, error) in
if let record = record {
self.currentChallenge = record
// edit and save record
} else {
print("error fetching challenge record from server", error!)
}
}
}
#IBAction func btnVote(_ sender: Any) {
// load record and save it to var existingChallengeToDetails
loadChallengeRecord()
}
The other two answers worked for the specific case, and work for many causes, but they weren't exactly what I was looking for. I kept running to similar issues and after some research I finally found what I was looking for: Semaphores
Here is a basic explanation:
func doSomething() {
let semaphore = DispatchSemaphore(value: 0) // Setup the semaphore to value:0
var x = 1
var y = 2
if y != 0 {
var sum = x + y
semaphore.signal(). // Sends signal that code is complete
// the code can continue from where semaphore.wait() is located.
}
semaphore.wait() // Wait for semaphore.signal() to fire, then continue to return
return sum // only after semaphore.signal() fires will this code run
}
Here is what I am trying to do:
var usernameCheckerResponse : String = ""
//This IBAction is a UITextfield that sends post request when editing is finshed.
#IBAction func usernameChecker(_ sender: Any) {
// perform post request with URLSession
// post request returns url response from URLSession
// the value of this response is either 'usernameExists' or 'usernameAvailable'
// usernameCheckerResponse = String(describing : response)
}
//use modified usernameCheckerResponse variable outside the IBAction function.
//For example like this:
func UsernameExists () -> Bool {
if(usernameCheckerResponse == "usernameExists"){
return true
} else { return false }
}
I am aware that an IBAction will only return a void, so is there anyway around this problem?
Any help and/or advice will be greatly appreciated.
Yes absolutely. Here is an example,
var usernameCheckerResponse : String = ""
//This IBAction is a UITextfield that sends post request when editing is finshed.
#IBAction func usernameChecker(_ sender: Any) {
//post request
// post request returns url response
// usernameCheckerResponse = String(describing : response)
}
//use modified usernameCheckerResponse variable outside the IBAction function.
func accessVariable() {
print("\(usernameCheckerResponse")
}
Keep in mind that the trick here is to access the variable when it has changed. To do that you need to pick some sort of way to keep track of that. Delegation is probably the most standard way to do that. See this. You would have to be more specific as to why you want the variable changed, because I would need to know what is using it (delegation required that you have are very specific on who is participating).
I would like to also be more specific with how delegation works. You would specify when the 'accessVariable()' function is called, in the place where you want the modified variable (this would always be between two different classes or structures). Keep in mind that you do not need to use delegation if you are just trying to share the variable in the same class. Calling the function 'accessVariable()' will suffice. However if this is the case where you want something to happen in the same class, but you really want to control in what order the functions finish then you need to use callbacks.
BTW Leo, doing it that way will make the app crash...
In general, you should think of IBAction functions as
connection points for controls like buttons etc.
You would never call it yourself.
If you need to do that, make another function
and have the IBAction function call that.
Since you are using URLSession to fetch the data from an external
source, you will need to be aware that this does not happen synchronously.
Send the call to your API and have the completion handler get called
when data is returned.
All of this code goes into your ViewController
// Set up a reusable session with appropriate timeouts
internal static var session: URLSession {
let sessionConfig = URLSessionConfiguration.default
sessionConfig.timeoutIntervalForRequest = 6.0
sessionConfig.timeoutIntervalForResource = 18.0
return URLSession( configuration: sessionConfig )
}
// Create an httpPost function with a completion handler
// Completion handler takes :
// success: Bool true/false if things worked or did not work
// value: String string value returned or "" for failures
// error: Error? the error object if there was one else nil
func httpPost(_ apiPath: String, params: [String: String], completion:#escaping (Bool, String, Error?) -> Void) {
// Create POST request
if let requestURL = URL( string: apiPath ) {
print("requestUrl \(apiPath)")
// Create POST request
var request = URLRequest( url: requestURL )
request.httpMethod = "POST"
var postVars : [String : String ] = params
var postString = postVars.toHttpArgString()
request.httpBody = postString.data( using: String.Encoding.utf8, allowLossyConversion: true )
let sendTask = ViewController.session.dataTask( with: request) {
(data, response, error) in
if let nserror = error as NSError? {
// There was an error
// Log it or whatever
completion(false, "", error)
return
}
// Here you handle getting data into a suitable format
let resultString = "whatever you got from api call"
// Send it back to the completion block
completion(true, resultString, nil)
}
sendTask.resume()
}
}
// I assume you have a text field with the user name you want to try
#IBOutlet weak var usernameToCheck : UITextField!
#IBAction func usernameChecker(_ sender: Any) {
guard let username = usernameToCheck.text else {
// This is unlikely to happen but just in case.
return
}
httpPost("https://someapicall", params: ["username" : username] ) {
(success, value, error) in
// This code gets called when the http request returns data.
// This does not happen on the main thread.
if success {
if value == "usernameExists" {
// User name already exists. Choose a different one.
DispatchQueue.main.async {
// put code here if you need to do anything to the UI, like alerts, screen transitions etc.
}
}
else if value == "usernameAvailable" {
// You can use this user name
DispatchQueue.main.async {
// put code here if you need to do anything to the UI, like alerts, screen transitions etc.
}
}
else {
// Unexpected response from server
}
}
else {
// Something did not work
// alert "Unable to connect to server"
}
}
}
To make this code work you will need this:
// Syntatic sugar to convert [String:String] to http arg string
protocol ArgType {}
extension String: ArgType {}
extension Dictionary where Key: ArgType, Value: ArgType {
// Implement using a loop
func toHttpArgString() -> String {
var r = String()
for (n, v) in self {
if !r.isEmpty { r += "&" }
r += "\(n)=\(v)"
}
return r
}
}
I am trying to get an array of temperatures in a given time period from an API in JSON format. I was able to retrieve the array through a completion handler but I can't save it to another variable outside the function call (one that uses completion handler). Here is my code. Please see the commented area.
class WeatherGetter {
func getWeather(_ zip: String, startdate: String, enddate: String, completion: #escaping (([[Double]]) -> Void)) {
// This is a pretty simple networking task, so the shared session will do.
let session = URLSession.shared
let string = "api address"
let url = URL(string: string)
var weatherRequestURL = URLRequest(url:url! as URL)
weatherRequestURL.httpMethod = "GET"
// The data task retrieves the data.
let dataTask = session.dataTask(with: weatherRequestURL) {
(data, response, error) -> Void in
if let error = error {
// Case 1: Error
// We got some kind of error while trying to get data from the server.
print("Error:\n\(error)")
}
else {
// Case 2: Success
// We got a response from the server!
do {
var temps = [Double]()
var winds = [Double]()
let weather = try JSON(data: data!)
let conditions1 = weather["data"]
let conditions2 = conditions1["weather"]
let count = conditions2.count
for i in 0...count-1 {
let conditions3 = conditions2[i]
let conditions4 = conditions3["hourly"]
let count2 = conditions4.count
for j in 0...count2-1 {
let conditions5 = conditions4[j]
let tempF = conditions5["tempF"].doubleValue
let windspeed = conditions5["windspeedKmph"].doubleValue
temps.append(tempF)
winds.append(windspeed)
}
}
completion([temps, winds])
}
catch let jsonError as NSError {
// An error occurred while trying to convert the data into a Swift dictionary.
print("JSON error description: \(jsonError.description)")
}
}
}
// The data task is set up...launch it!
dataTask.resume()
}
}
I am calling this method from my view controller class. Here is the code.
override func viewDidLoad() {
super.viewDidLoad()
let weather = WeatherGetter()
weather.getWeather("13323", startdate: "2016-10-01", enddate: "2017-04-30") { (weatherhandler: [[Double]]) in
//It prints out the correct array here
print(weatherhandler[0])
weatherData = weatherhandler[0]
}
//Here it prints out an empty array
print(weatherData)
}
The issue is that API takes some time to return the data, when the data is return the "Completion Listener" is called and it goes inside the "getWeather" method implementation, where it prints the data of array. But when your outside print method is called the API hasn't returned the data yet. So it shows empty array. If you will try to print the data form "weatherData" object after sometime it will work.
The best way I can suggest you is to update your UI with the data inside the "getWeather" method implementation like this:
override func viewDidLoad() {
super.viewDidLoad()
let weather = WeatherGetter()
weather.getWeather("13323", startdate: "2016-10-01", enddate: "2017-04-30") { (weatherhandler: [[Double]]) in
//It prints out the correct array here
print(weatherhandler[0])
weatherData = weatherhandler[0]
// Update your UI here.
}
//Here it prints out an empty array
print(weatherData)
}
It isn't an error, when your controller get loaded the array is still empty because your getWeather is still doing its thing (meaning accessing the api, decode the json) when it finishes the callback will have data to return to your controller.
For example if you were using a tableView, you will have reloadData() to refresh the UI, after you assign data to weatherData
Or you could place a property Observer as you declaring your weatherData property.
var weatherData:[Double]? = nil {
didSet {
guard let data = weatherData else { return }
// now you could do soemthing with the data, to populate your UI
}
}
now after the data is assigned to wheaterData, didSet will be called.
Hope that helps, and also place your jsonParsing logic into a `struct :)
So I have a function I have that has an inner function that connects to a Firebase database. the function returns a bool but I need the to return true or false based on whats inside the Firebase database. So basically I need to return true or false inside of the Firebase function the problem is it thinks that I am trying to return to the Firebase function when I am actually trying to return to the outside function a simple example is this
func someOtherFunc(name: String, lastname: String){
}
func someFunc(name: String, lastname: String) -> bool {
someOtherFunc(name: name, lastname: lastname) {
if name == "George" {
return true
} else {
return false // will not work because some other func does not return a value
}
}
}
here is the code that I need fixed which is a little more complicated than the above function because the inner Firebase function runs asynchronously(in the background) and so all the code inside the function needs to run synchronously to return the correct value
Here is my function
func takeAwayMoney(_ howMuch: String) -> Bool{
if let notMuch = Int(howMuch) {
let userID = FIRAuth.auth()?.currentUser?.uid
datRef.child("User").child(userID!).observeSingleEvent(of: .value, with: { (snapshot) in
// Get user value
let value = snapshot.value as? NSDictionary
let money = value?["money"] as? String ?? ""
//convert money to int
if let conMoney = Int(money) {
var conMoreMoney = conMoney
if conMoreMoney < notMuch {
print(" sorry you don't have enough money")
return false
} else {
conMoreMoney -= notMuch
let values = ["money": String(conMoreMoney)]
//update the users money
self.datRef.child("User").child(userID!).updateChildValues(values)
return true //doesn't work because of example above
}
}
// ...
}) { (error) in
print(error.localizedDescription)
}
}
}
This code does not compile because there is no return values to the main function.
I know the really hard way to fix this would be to initialize values at the top of the function that would be the money of the user then check it after dispatching it for a couple of seconds then you could return the values, but I know there must be another way because this way would cause a lot of problems.
The root cause is that takeAwayMoney is synchronous, but it uses observeSingleEvent, which is asynchronous.
The "right" way to solve this is to make takeAwayMoney return Void, but take a completion function that will give you the bool asynchronously, like this:
func takeAwayMoney(_ howMuch: String, completion: #escaping (Bool)->()) -> Void {
/// When you want to "return" the bool, call the completion. e.g.:
// ...
if conMoreMoney < notMuch {
print(" sorry you don't have enough money")
completion(false)
return // if you want to stop processing
}
// ...
}
If you cannot do this, then takeMoney needs to wait for the completion to finish and you use semaphores to have them communicate with each other. You do not just wait a couple of seconds. See this for an example:
Semaphores to run asynchronous method synchronously
I'm pretty new to IOS Application Development.
I'm trying to stop viewWillAppear from finishing until after my function has finished working. How do I do that?
Here's viewWillAppear:
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(true)
checkFacts()
if reset != 0 {
print("removing all bird facts")
birdFacts.removeAll()
}
}
func checkFacts() {
let date = getDate()
var x: Bool = true
var ind: Int = 0
print("count is ", birdFacts.count)
while ind < birdFacts.count {
print("accessing each bird fact in checkFacts")
let imageAsset: CKAsset = birdFacts[ind].valueForKey("birdPicture") as! CKAsset
let image = UIImage(contentsOfFile: imageAsset.fileURL.path!)
print(image)
if image == nil {
if (birdFacts[ind].valueForKey("sortingDate") != nil){
print("replacing fact")
print("accessing the sortingDate of current fact in checkFacts")
let sdate = birdFacts[ind].valueForKey("sortingDate") as! NSNumber
replaceFact(sdate, index: ind)
}
/*else {
birdFacts.removeAll()
print("removing all bird facts")
}*/
}
ind = ind + 1
print(ind)
}
self.saveFacts()
let y = checkRepeatingFacts()
if y {
print("removing all facts")
birdFacts.removeAll()
//allprevFacts(date, olddate: 0)
}
}
checkFacts references 2 others functions, but I'm not sure they're relevant here (but I will add them in if they are and I'm mistaken)
Instead of trying to alter or halt the application's actual lifecycle, why don't you try using a closure?
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(true)
checkFacts(){ Void in
if self.reset != 0 {
print("removing all bird facts")
birdFacts.removeAll()
}
}
}
func checkFacts(block: (()->Void)? = nil) {
let date = getDate()
var x: Bool = true
var ind: Int = 0
print("count is ", birdFacts.count)
while ind < birdFacts.count {
print("accessing each bird fact in checkFacts")
let imageAsset: CKAsset = birdFacts[ind].valueForKey("birdPicture") as! CKAsset
let image = UIImage(contentsOfFile: imageAsset.fileURL.path!)
print(image)
if image == nil {
if (birdFacts[ind].valueForKey("sortingDate") != nil){
print("replacing fact")
print("accessing the sortingDate of current fact in checkFacts")
let sdate = birdFacts[ind].valueForKey("sortingDate") as! NSNumber
replaceFact(sdate, index: ind)
}
/*else {
birdFacts.removeAll()
print("removing all bird facts")
}*/
}
ind = ind + 1
print(ind)
}
self.saveFacts()
let y = checkRepeatingFacts()
if y {
print("removing all facts")
birdFacts.removeAll()
//allprevFacts(date, olddate: 0)
}
// CALL CODE IN CLOSURE LAST //
if let block = block {
block()
}
}
According to Apple Documentation:
Closures are self-contained blocks of functionality that can be passed around and used in your code.
Closures can capture and store references to any constants and variables from the context in which they are defined.
So by defining checkFacts() as: func checkFacts(block: (()->Void)? = nil){...} we can optionally pass in a block of code to be executed within the checkFacts() function.
The syntax block: (()->Void)? = nil means that we can take in a block of code that will return void, but if nothing is passed in, block will simply be nil. This allows us to call the function with or without the use of a closure.
By using:
if let block = block {
block()
}
we can safely call block(). If block comes back as nil, we pass over it and pretend like nothing happened. If block is not nil, we can execute the code contained within it, and go on our way.
One way we can pass our closure code into checkFacts() is by means of a trailing closure. A trailing closure looks like this:
checkFacts(){ Void in
if self.reset != 0 {
print("removing all bird facts")
birdFacts.removeAll()
}
}
Edit: Added syntax explanation.
So based on the comments, checkFacts is calling asynchronous iCloud operations that if they are not complete will result in null data that your view cannot manage.
Holding up viewWillAppear is not the way to manage this - that will just result in a user interface delay that will irritate your users.
Firstly, your view should be able to manage null data without crashing. Even when you solve this problem there may be other occasions when the data becomes bad and users hate crashes. So I recommend you fix that.
To fix the original problem: allow the view to load with unchecked data. Then trigger the checkData process and when it completes post an NSNotification. Make your view watch for that notification and redraw its contents when it occurs. Optionally, if you don't want your users to interact with unchecked data: disable appropriate controls and display an activity indicator until the notification occurs.